The present invention relates to protective layering for fiber optics. In particular the invention relates to protective layers which protect optically transmissive fibers from corrosion and the resulting degradation of optical properties and loss of tensile strength in environments where fluids under conditions of high pressure or temperature in geophysical or deep sea explorations create a corrosive effects.
Optical fibers for transmitting light information are typically formed in an optical fiber cable containing one or more light transmitting optical fibers comprised of a glass core and cladding with optional protective coatings of polymeric buffers, metals, metal oxides or nitrides and others. These protective coating materials are often carried in a thin outer covering layer over the cladding. Surrounding the fiber a polymeric buffer is usually provided and its adherence to the underlying fiber may be enhanced by the inclusion of a layer of coupling agents between the fiber and buffer. Surrounding the buffer may be one or more additional protective layers which may be polymerized, braided or woven about the fiber.
Even the best of coverings for an optical fiber will slowly absorb and transmit to the fiber environmental fluids such as water, hydrogen sulfide, acids or bases, particularly under high temperature and pressure. The slow but nevertheless persistent penetration of these environmental substances through the outer layers will, over time, result in the corrosion of the inner fiber destroying not only its tensile strength but its optical transmission properties.
Any attempt to provide protective layering for the optical fiber must avoid increasing the microbending loss of the fiber resulting from the location of inhomogeneous materials directly adjacent to the optically transmitting fiber. It is also important that the protecting layers avoid being structured so that they are, or under environmental influences become, highly porous and thereby more rapidly admit under certain circumstances the corrosive environmental materials.